Studies are being carried out to further define the nature of functional and structural changes during development. These studies are being carried out in newborn dogs, rats, rabbits, pigs and include both in vivo and in vitro techniques. Some of the determinations include organic anion and cation transport, total and regional renal blood flow, acid base balance, electrolyte excretion and secretion of renin and prostaglandins. Quantitative assessment of diuretic efficacy and measures of preliminary and renal angiotensin converting enzyme are also being conducted.